1. Technical Field
The present invention relates generally to miniature hearing aids, acoustic and otherwise, which are fitted deeply in the ear canal.
2. Description of the Prior Art
Conventional hearing aids provide sound amplification selected based on individual hearing loss. It is well known in the field of hearing aids that turning such devices OFF while being worn in the ear causes additional hearing loss to the wearer. This loss, referred to sometimes as “insertion loss”, occurs due to the occlusion of the ear canal by the hearing device. This occlusion prevents sounds from reaching the eardrum directly via the ear canal (see e.g., Sandlin, Hearing Instrument Science & Fitting Practices, National Institute for Hearing Instruments Studies, 1996, pp. 358).
It is also well known in the field of hearing aids that the unoccluded (open) ear canal (1 in FIG. 1) contributes significantly to the acoustic modification which occurs when sound (2) travels to the eardrum (4). This transfer function, sometimes referred to as Real-Ear Unaided Response (REUR) which includes the canal resonance, provides acoustic amplification at certain frequencies, generally in the range of 2000 to 4000 kHz (see e.g., Chasin M., Completely In The Canal Handbook, Singular Publishing, 1997, pp. 91). However, the occlusion by an in-situ hearing device in the OFF condition dramatically alters both the quality of incoming sound (altered frequency response—muffled) as well as its quantity (attenuation).
For the above reasons, a hearing aid is typically either worn with amplification ON, or removed from the ear and turned OFF for conserving battery power. It is conceivable that a hearing device may be worn OFF for achieving sound attenuation with the device acting essentially as an earplug. However, this is clearly not a desirable scenario for the hearing impaired who already suffer from hearing loss and cannot afford the additional loss. An acoustic vent across a hearing device is typically employed in conventional aids for variety of reasons including allowing certain frequency ranges to bypass the device and reach the eardrum via the vent. However, venting is useful mainly in conjunction with amplification provided by the ON in-situ device. Hence, vents do not substitute for the natural unaided response when an in-situ device is in the OFF condition.
More practical means of reducing current consumption, without resorting to shutting of the device, include volume reduction. However, volume reduction does not reduce power consumption proportional to the reduction nor does it restore the natural perception of unaided hearing.
Reducing the power consumption has always been a major goal in hearing aid design. In programmable hearing aids, for example, circuit elements can be selectively turned off depending on the operating condition required by the user. Martin et. al. for example, in U.S. Pat. No. 5,710,820 describe a hearing aid in which “function blocks not required for the selected operating condition are deactivated and bridged (cut out), so that only the current respectively required for the active function blocks is drawn from the battery 35.”
Recent advances have lead to the development of extended-wear (semi-permanent) canal hearing devices, which are operated continuously in the ear canal for several months before battery depletion and removal. These canal hearing devices are totally inconspicuous thus cosmetically appealing to the users. Turning these extended-wear devices OFF during sleep or inactivity is desirable on one hand for reducing power consumption and extending the battery life of the device. However, turning these devices OFF in-situ causes an insertion loss as described above. The insertion loss is problematic for these users since it further limits their hearing ability , particularly in emergency situations (fire alarm, horn blowing, traffic sounds, etc.). Another problem caused by the insertion loss of hearing aids in general is the inability to hear sounds naturally in a similar manner as in the unaided condition. Removal of the extended-wear devices to restore unaided hearing contradicts the intended purpose of their continuous wear.
A key goal of the present invention is to provide a canal device and a method thereof for reproducing the unaided response while the hearing device is worn in the ear canal.
Another goal of the present invention is to significantly reduce the power consumption of a canal hearing device in-situ while simultaneously producing the experience of unaided hearing.